The present invention relates to a papermaking felt used for a papermaking machine (hereinafter occasionally referred to as simply a “felt”) and a method for producing the same.
A papermaking machine that removes water from the source material of paper generally includes a wire part, a press part, and a drier part. The wire part, the press part, and the drier part are arranged in this order along the wet paper web conveyance direction. The wet paper web moves through the papermaking machine in a band shape, with a certain width in the direction (cross-machine direction, CMD) perpendicular to the running direction of the papermaking machine (machine direction, MD), and is conveyed to be squeezed to remove water and finally dried in the drier part while being sequentially passed through the papermaking equipments provided in the wire part, the press part, and the drier part.
The press part comprises a plurality of press apparatuses that is provided side by side in series along the wet paper web conveyance direction. Each press apparatus comprises an endless felt or a felt, in which ends of an ended felt are connected on the papermaking machine into an endless shape, and a pair of rolls (i.e., a roll press), which are arranged facing each other in the vertical direction to sandwich a part of the felts, or a cylindrical belt comprising a roll and a shoe (i.e., a shoe press), and uses the felt together with the rolls or the cylindrical belt including a roll and a shoe to press and apply pressure to the wet paper web conveyed by the felt running at a substantially constant speed in the fixed direction and thus dehydrates the wet paper web continuously.
Water squeezing capability, smoothness, running stability, etc. are required as functions for the felt used for the press apparatus. The water squeezing capability refers to a capability to remove water contained in the wet paper web. To achieve this function, it is important that the felt have a good compression recovery property, that is, when the felt is not under pressure, a space (void volume) for removing the water of the felt exist in the felt, and when the felt is under pressure, the density of the felt be maximized and the volume of the space be reduced to discharge the water to the outside of the felt. It is also important that the water squeezing capability be maintained during a period of use of the felt and that the removed water be not return to the wet paper web (re-wetting prevention).
The smoothness refers to the smoothness of the surface of the wet paper web and the surface of the felt (including the surface of the felt under pressure). Since the wet paper web is pressed via the felt, the surface condition of the felt is transferred to the surface of the wet paper web. Hence, to smooth the surface of the wet paper web, it is necessary to smooth the surface of the felt (including the surface of the felt under pressure).
The running stability refers to the capability of the endless felt placed in the press apparatus to run stably without the occurrence of deviation, meandering, vibration, waving, etc.
There are various kinds of paper, such as paper for newspapers, high-quality paper, paperboards, and household paper, and there are also various kinds of papermaking machines that produce these kinds of paper. Various kinds of papermaking felt are currently produced to fit these kinds of paper and papermaking machines; in general, the felt is formed by integrating a batt layer of a nonwoven fiber material with a base fabric layer. The base fabric layer may be, for example, a woven fabric formed of monofilament yarns, monofilament twisted yarns, multifilament yarns, or multifilament twisted yarns, and the woven fabric may be a single-woven article or a multiple-woven article, or may be a laminated structure, in which these are laminated together. The yarn can be usually made of a material produced by extrusion-molding a synthetic polymer resin that a person skilled in the technical field of papermaking equipments uses for this objective, such as a polyamide resin or a polyester resin, or animal fibers such as wool or vegetable fibers such as cotton or hemp.
As the base fabric layer mentioned above, there are various kinds of woven fabric, such as one in which weaving is performed on a weaving machine to obtain an endless shape (hollow weaving), one in which ends of an ended woven fabric obtained by plain weaving are sewn together into an endless shape, and one in which seam loops are formed at each of the two ends in the cross-machine direction of an ended woven fabric, the seam loops at both ends are engaged with each other on a papermaking machine, and a core line is inserted into their common holes to form an endless shape.
In any case, the base fabric layer has an endless form or is configured to allow its ends to be joined together into an endless form, and the length dimension and the width dimension of the base fabric layer (felt) are dimensions corresponding to each papermaking machine. Since the papermaking machines have various dimensions, the base fabric of the felt is produced completely in a made-to-order manner as a matter of course.
In the case where base fabric layers matched with various dimensions are woven with a weaving machine, the productivity is very poor and the yield is poor. In order to produce these base fabric layers more efficiently, a method in which a band-shaped body with a width smaller than the width dimension of the papermaking felt is spirally wound, the ends of the band-shaped body are joined together, and the base fabric formed is used as the base fabric layer of the papermaking felt is proposed (e.g. JP H06-503385T, JP H10-226978A, JP 2000-027089A, JP 2000-303378A, JP 2001-040594A, JP 2004-510896T, JP 2004-526877T, and JP 2006-504873T). Further, a method in which a band-shaped body narrower than the width dimension of the papermaking felt is spirally wound, the ends of the band-shaped body are joined together, the base fabric formed is folded, and a seam loop is formed at the fold (e.g. JP H10-513511T, JP 2000-080585A, JP 2000-080586A, and JP 2005-521807T), and a method in which a band-shaped body narrower than the width dimension of the papermaking felt is spirally wound, the ends of the band-shaped body are joined together, and the formed base fabric and an endless base fabric are laminated together (e.g. JP 2000-509772T, JP 2000-080584A, and JP 2001-003290A) are proposed.